1. Field of the Invention
The subject invention pertains to novel macromers for the preparation of graft polyether polyols. Such graft polyether polyols have extensive uses in polyurethane technology.
2. Description of the Related Art
Graft polyether polyols are prepared by the in situ polymerization of one or more unsaturated monomers in a polyether polyol. Acrylonitrile and styrene are the most commonly used monomers. If appreciable polymer content and low viscosity are desirable, the polyol must contain a dispersion stabilizer. This latter is the true graft polyol and exerts a steric effect between the dispersed polymer phase and the continuous polyol phase which helps maintain the dispersed phase in suspension. Thus the graft polyol acts as a steric stabilizer. See, for example, Dispersion Polymerization in Organic Media, K. Barrett, Ed., John Wiley & Sons c1975, especially at pages 74ff and 130ff.
Macromers which are useful as the starting material for stabilizers may be prepared, for example, as taught in U.S. Pat. No. 4,550,194. In this reference polyether polyol having hydroxyl termination is reacted with maleic or fumaric acid or one of their derivatives, preferably maleic anhydride. Any maleate unsaturation is isomerized to fumarate, and the acid group present in the half ester formed from the reaction may be removed by capping with an alkylene oxide, reducing the acid number of the polyol to zero or thereabouts. The resultant unsaturation-containing polyether polyol is termed a macromonomer or a macromer. Upon addition of one or more unsaturated monomers, vinylic polymers become grafted onto the macromer, forming dispersion stabilizers having the attributes of both vinyl polymers and polyether polyols. At the same time the dispersion stabilizer is being formed from reaction of the vinyl monomer(s) with the macromer, polymerization of the vinyl monomers proceeds, forming the polymer dispersed phase. Using this technology, graft polymer dispersions having low viscosities and polymer contents above 50 weight percent may be prepared, particularly when a reaction moderator is also present.
However, the preparation of the macromer presents certain difficulties. First, the cycle time is quite long, typically from 15-30 hours. This results in inefficient use of expensive production equipment. Second, the preparation of the macromer is very sensitive to contamination. For this reason, macromers derived from polyols having amine functionality, for example polyoxyalkyenepolyamines, or polyols containing traces of amines, are difficult to make by prior art processes. The prior art macromers generally also have relatively high viscosities, for example, greater than 7000 cP. This higher viscosity may cause a concomittant increase in the viscosity of the graft polyol prepared therefrom. In general, lower viscosity polyols are easier to process when preparing polyurethanes. Finally, the conventional macromer synthesis is inefficient, yielding a macromer containing only about 50-70 percent of the theoretical induced unsaturation, with the remainder undergoing dimer and higher oligomer formation through Michael addition reactions.
In U.S. Pat. No. 4,581,418, are disclosed reactive ethylenically unsaturated moieties of the formula EQU X--CHR.sub.1 =CHR.sub.2
which may be reacted with polyether or polyester polyols by virtue of a reactive group X which may be, by way of example, carboxylic acid or anhydride, epoxy, or isocyanate, with isocyanates, for example isocyanatoethylmethacrylate, being preferred. However, the use of such compounds to induce unsaturation into the polyol creates unsaturation-containing-macromers which are chemically very reactive and which must be used directly after preparation. There is no possibility, for example, of preparing a large batch of macromer and then utilizing it as the need arises.